I told soon to be exH that I'd had enough of his snoring, it was affecting my ability to function, and that I would leave if he didn't do something about it (this was after lots and lots of "discussions" about it where he claimed it was me that had a problem with insomnia and I should go to the doctor!).
He did then go to the GP, who referred him to the sleep clinic, where they discovered that he had pretty bad sleep apnea, and couldn't understand how he wasn't falling asleep during the day. He got a CPAP machine, and after a few weeks, admitted that actually yes, he was sleeping a lot better, and maybe yes, his snoring had been a problem.
Annoyingly, the consultant had told him that telling people with sleep apnea to "just lose weight" didn't really work (from a psychological perspective), which he took to mean that his weight wasn't an issue at all, and he didn't need to do anything about it. So his weight went up, and the snoring started back again, although not nearly as bad as before. He was very resentful of me "making" him sort it out in the first place, and "nagging" him about cleaning all the different bits (so he wasn't breathing in gunky stuff all night), and while it wasn't the cause of us splitting up, his attitude to it all certainly didn't help.